Research On The Causes Of Deactivation And Regeneration Methods Of Zn Catalysts For Acetylene Acetoxylation

Vinyl acetate is one of the most used chemical production materials in the world and has a very wide range of applications in the fields of coatings,adhesives,fiber synthesis,and processing leather.The methods of preparing vinyl acetate mainly include calcium carbide acetylene method and petroleum ethylene method.Due to the characteristics of chinese oil-poor,gas-poor and coal-rich energy structure,it is decided that the synthesis of vinyl acetate by calcium carbide acetylene method has a very broad development prospect in the coal-rich areas in western China.In view of the problems of low conversion,easy carbon accumulation and loss of active component in the current industrialized activated carbon loaded zinc acetate catalysts,there is an urgent need to research and develop new novel high-performance catalysts for acetylene acetoxylation.This experiment is dedicated to improve the catalyst utilization rate and to solve the influence of carbon deposition on the catalyst performance on the basis of ensuring catalytic performance,and to study the regeneration of catalyst by removing carbon deposition and reducing the loss of active component.（1）The catalysts were prepared by the impregnation method using zinc acetate dihydrate as the precursor of the active component Zn and activated carbon as the carrier.The catalysts were further treated by controlling the calcination temperatures（300℃,500℃and 800℃）and calcination atmospheres（air,nitrogen and hydrogen）to improve the catalyst performance and applied to the acetylene acetoxylation.It was found that the catalysts treated under calcination temperature of 500℃and nitrogen atmosphere had the most excellent catalytic performance.Characterization by XRD,TEM,XPS demonstrated that the active component Zn existed in the catalyst in the form of ZnO,and the content of oxygen-containing functional groups（OCGs）carboxyl group（-COOH）on the surface of the activated carbon carrier was relatively increased by calcination,thus improving the catalyst performance.（2）Based on the previous experiments,we considered calcination at 500°C in air atmosphere to remove the carbon deposition,but the activated carbon carrier would burn with the carbon deposition during calcination,so we chose 3A molecular sieve carrier with excellent high temperature stability as the model for the study.In this study,ZnO/3A catalysts were prepared by one-step hydrolysis,and it was found that the acetic acid conversion of ZnO/3A was lower than that of ZnO/AC due to the weak adsorption of acetylene.The catalysts were regenerated by removing the carbon deposition on the ZnO/3A,but we found that the performance of the regenerated catalysts did not return to the ideal state.By characterizing the fresh,deactivated and regenerated ZnO/3A,it was found that the loss of the active component Zn was the main reason for its deactivation,while carbon deposition did not affect the catalytic performance of the ZnO/3A.（3）The ZnO/Fe₂O₃ catalyst was prepared by one-step hydrolysis method,and the optimal loading of Zn was screened.It was found that ZnO/Fe₂O₃ had higher acetic acid conversion than ZnO/3A,and the loss rate of Zn was found to be lower than that of ZnO/3A by ICP test.The regeneration experiment of ZnO/Fe₂O₃ was carried out and the fresh,deactivated,regenerated catalysts were characterized by XRD,TG and ICP.It was found that the deactivation of ZnO/Fe₂O₃ is also caused by the loss of active component Zn,and it is proved that Fe₂O₃ can exist stably in the reaction and regeneration process.Carbon deposition can also be successfully removed in the regeneration process.